ligo's first observing run: gravitational-wave astronomy on the rise
TRANSCRIPT
LIGO's First Observing Run: Gravitational-Wave Astronomy on the Rise
Chris Pankow (CIERA / Northwestern University) on behalf of the LIGO Scientific Collaboration and Virgo Collaboration
LIGO-G1601533ICHEP: August 6, 2016
GW Available in this Talk
• The LIGO and Virgo Collaborations: 1000+ scientists, engineers, and others spread amongst 50+ academic institutions world wide (presence on all continents except Africa and Antarctica)
• Collectively develop and operate a network of three kilometer scale interferometers (LIGO Hanford, LIGO Livingston, Virgo), and a 600m pathfinder interferometer (GEO600)
• Two kilometer scale interferometers under construction (KAGRA collaboration, Japan) or in design process (LIGO India)
The LVC: Who We Are2
R. Williams (Caltech)
In Case You Hadn’t Heard...
GW150914
“We.. have... detected gravitational waves... We did it!” — Dave Reitze, LIGO Lab Director (February 11, 2016)
3
https://losc.ligo.org/events/GW150914/
Advanced LIGO’s First Observational Run4
C. North (Cardiff)
LIGO Livingston
LIGO Hanford
The Instruments: two near-identical 4 km long Fabry-Perot
dual-recycled laser interferometers
Strain: Differential phase measurement of highly coherent laser beams
translated from perturbations of space-time curvature at the level of 10-18 m along
arms
Advanced LIGO’s First Observational Run5
Seismic motion shot noise
power linecouplings
calibrationlines
Low Frequency: motion of the Earth coupling into motion of
the end test masses
High Frequency: uncertain photon arrival times at
photodetector
Monochromatic Lines: calibration lines, 60 Hz power
line and harmonics thereof
GW Signal Detection Primer6
Putative strain is embedded in detector noise — cross correlate the model with the data to extract a signal-to-
noise ratio (SNR, ρ) statistic — this maximizes the likelihood (probability of signal vs probability of noise)
Searches maximize likelihood analytically for speed and
over masses/spins by brute force (template banks)
arxiv:1606.04856
d(t) = h(t) + n(t)
GW Signal Detection Primer7
Putative strain is embedded in detector noise — cross correlate the model with the data to extract a signal-to-
noise ratio (SNR, ρ) statistic — this maximizes the likelihood (probability of signal vs probability of noise)
Searches maximize likelihood analytically for speed and
over masses/spins by brute force (template banks)
arxiv:1606.04856
d(t) = h(t) + n(t)
O1 BBH Events8
“Chirps” in the time domain (monotonically increasing in frequency vs time)
Lower mass → Higher frequency content / longer “in band”
arxiv:1606.04856
BBH Masses and Spins9
Parameter Degeneracies: Primarily sensitive to the chirp mass
— leaves large degeneracies along contours of chirp mass
(GW151226 approaching m2 < 3 region)
Frequency content (and thus “length in band” affected by both effective spin and mass
ratio at same order in expansion of radiation
amplitude/phase
equal mass
equa
l mas
s
arxiv:1606.04856
BBH Masses and Spins10
equal mass
equa
l mas
s
Cosmological Effects:All events at distances with
significant redshifts — all masses need to be adjusted to account for
frequency “stretching” from GW traversing expanding universe
Precession?GW151226 has posterior on “in plane spin” component bounded
away from zero — spin-orbit coupling causes plane of binary to
precess around total angular momentum. Also, at least one BH must be a Kerr black hole (as are
the final remnants in all cases)Phys. Rev. Lett. 116/241103
BBH Detection11
Signal and Background (Higgs):For a given decay channel (4 lepton), this
shows the background levels and expected Higgs signal decay rates along with the data collected — clear statistical
excess ~125 MeV
Signal and Background (GW):Different parameterization, using a likelihood ranking statistic modeling
background with the expected volumetric (ρ-4) distribution superimposed
arxiv:1606.04856
Phys. Lett. B (716) 1Phys. Lett. B (716) 1
BBH Detection12
Signal and Background (Higgs):For a given decay channel (4 lepton), this
shows the background levels and expected Higgs signal decay rates along with the data collected — clear statistical
excess ~125 MeV
Signal and Background (GW):Different parameterization, using a likelihood ranking statistic modeling
background with the expected volumetric (ρ-4) distribution superimposed
arxiv:1606.04856
Phys. Lett. B (716) 1Phys. Lett. B (716) 1
BBH Detection13
Towards Measuring Mass Distributions:
Posterior distribution for exponent of m1 inferred from three astrophysically
distinguished events — note peak very close to α = 2.35 (black vertical line)
arxiv:1606.04856
Signal and Background (GW):Different parameterization, using a likelihood ranking statistic modeling
background with the expected volumetric (ρ-4) distribution superimposed
Dealing with Multiple Event Categories:Being unsure of the intrinsic source populations and origins, we calculate the event rates for
all three events and take the union to derive the overall event rate of BBH coalescence. Also test distributions of events according to uniform in the logarithm of component mass
and according to the stellar initial mass function: p(m1) ∝ m12.35
BBH Event Rates14
arxiv:1606.04856
Dealing with Multiple Event Categories:Being unsure of the intrinsic source populations and origins, we calculate the event rates for
all three events and take the union to derive the overall event rate of BBH coalescence. Also test distributions of events according to uniform in the logarithm of component mass
and according to the stellar initial mass function: p(m1) ∝ m12.35
BBH Event Rates15
arxiv:1606.04856
Astrophysics Implications16
Ap. JL. L22 2016
Astrophysics Implications17
Ap. JL. L22 2016
Astrophysics Implications18
Ap. JL. L22 2016
In Context19
Lower Mass (X-ray Binaries)
Some near maximal spin (> 0.9)
GW150914aGW150914bGW150914GW151226aGW151226bGW151226LVT151012aLVT151012bLVT151012
6035 40 45 50 ~
Higher Mass (GW)spins constrained mostly below
maximum
https://stellarcollapse.org/bhmasses
BNS / NSBH Upper Limits20
Compact Sources: Only BBH detections so far, NSBH and BNS remain elusive, but
expected to constrain models in the next year
https://arxiv.org/abs/1607.07456201520162017 201520162017
Testing GR21
The single-parameter analysis corresponds to minimally extended models, that can capture deviations from GR that predominantly, but not
only, occur at a specific PN order
Graviton Mass: Confined Compton wavelength > 1013 km (best dynamical bound), by testing dispersion in the expected
frequency content of the waveform
Expand Einstein’s equations in velocity (PN order) and
introduce deviations — use MCMC to test for phase
evolution deviations from GR
arxiv:1606.04856
Sky Localization22
Sky Localization: Two detectors with coherence still restricted to partial annulus on
sky
Observation Biases: Optimal location for single detector:
directly overhead — preference to detect over North America
and Indian Ocean
https://arxiv.org/abs/1602.08492
Sky Localization23
Sky Localization Timeline: Sky position information
released within two days — huge follow up program
followed thereafter
Towards Joint Astronomy: If a binary with a neutron star
component is detected, possibility of multi-wavelength
electromagnetic emission as well!
prompt
hours/days
weeks
possible EM emissionduration
https://arxiv.org/abs/1602.08492
O2 and Beyond24
GW150914 in 2018: Events like GW150914 could have SNR 40 / detector with total SNR ≲ 100 (three detectors)
GW150914 in 2018: Events like GW150914 will have
SNR 40 / detector with total SNR <=100 (three
detectors)
O2 and Beyond25
Future Detections: Depending on sensitivity,
could optimistically see tens of BBH in O2, perhaps x2
in O3?
Finally...26
Stay tuned for talk by Lisa Barsotti for the exciting details on how these feats are accomplished with laser interferometry
and the future of the experiment
A. Simonnet (Sonoma State)
Come visit us and see our GW data releases: https://losc.ligo.org/about/
GW150914 Fun Facts
GW15094 Lpeak ~ 50 visible universes
GW150914 ∫ L(t) dt ~ 1054 TeV (3
M☉ c2)